1. Field of the Invention
The present invention relates to a high-frequency signal amplifier that operates mainly in microwave regions and milli-wave regions.
2. Background Art
With the popularization of the mobile wireless equipment such as mobile phones, the technical advantages of high-frequency signal amplifiers and antennas have been desired. Furthermore, impedance matching between the load of the high-frequency signal amplifier and the load of the antenna is required so that the electric power of the desired high-frequency signal is supplied to the antenna from the high-frequency signal amplifier.
However, depending on the situation of the mobile wireless equipment, the load of the antenna varies. For example, depending on a situation such as where the mobile phone is covered with a hand, placed on an insulator, placed on a conductor, or hung in the air, the load of the antenna varies. Therefore, there was a problem that intended impedance matching could not be realized, and sufficient electric power for high-frequency signals could not be supplied to the antenna.
Therefore, it has been proposed that a detector for detecting the load of the antenna, a variable capacitance, and an integrated circuit for controlling to apply voltage to the variable capacitance depending on the load of the antenna are provided for the output terminal of the high-frequency signal amplifier (for example, see Non-Patent Literatures 1 to 3). Thereby, by varying impedance depending on change in the load of the antenna, the electric power of the high-frequency signal to be supplied to the antenna can be held constant.
Non-Patent Literatures 1: “Mobile Phone Performance Improvements using an Adaptively Controlled Antenna Tuner,” 2011 IEEE MTT-S Int. Microwave Symposium Digest, June 2011
Non-Patent Literatures 2: “CMOS Based Tunable Matching Networks for Cellular Handset Applications,” 2011 IEEE MTT-S Int. Microwave Symposium Digest, June 2011
Non-Patent Literatures 3: “High Performance Tuners for Handsets,” 2011 IEEE MTT-S Int. Microwave Symposium Digest, June 2011